Martin McDonagh (The Pillowman) cribs shamelessly from hyperviolent indie caper films, overdoes the Grand Guignol sanguinary spray, and indulges his psychotic characters with Tarantinoesque gunpoint ramblings — all things a formal education would have drummed out of him. Fortunately, McDonagh never had a formal education. The Lieutenant of Inishmore, the second play in his Aran Islands trilogy — focusing on a ferociously inept IRA splinter group and the disastrous assassination of a pet cat — was written in the mid-’90s, but it’s a mordant, marvelous, and all-too-current comedy of terror.